The device of this invention relates to a full charge detection circuit for a battery changing circuit which detects electrically the temperature rise occurring at the time of full charge of the battery by means of a temperature detection element and activates an alarm when the charge is complete or cuts off the power source.
Detection of the full charge of a battery has conventionally been made by the following methods.
(1) A method which detects a voltage drop across terminals of the battery at the time of full charge;
(2) A method which turns off charging by setting a charging time in advance;
(3) A method which detects the temperature rise value of the battery at the time of full charge; and
(4) A method which sets in advance a maximum value of the voltage rise because the terminal voltage of the battery rises at the time of full charge, and detects the maximum value so set.
The applicant is also aware of the battery charging systems disclosed in the following U.S. Pat. Nos.: 3,895,283; 3,667,026; 3,579,075; 3,518,524; 2,967,988; 2,529,038; 2,402,695; 2,369,826; 976,750 and 976,747.
However, none of these methods are entirely satisfactory for the accurate detection of the full charge time because setting of the temperature or the voltage at the time of full charge fluctuates depending upon the change in the ambient temperature or in the discharge quantity of the battery and pre-setting of the charging time can not be made so accurately. In view of these problems, the device of the present invention enables the accurate detection of the full charge time by detecting the temperature difference arising from the temperature rise at the time of full charge.